CHAPTER XI
THE PRACTICAL MANIPULATION OF A LANTERN
Having now described the optical lantern in its various forms and the more important accessories, we come to the question of practical manipulation. In making arrangements for an exhibition the first thing to be seen to is to ensure that every accessory that will be required will be there, and the best plan is to make a complete list of all sundries to be provided. Such items as string (for the sheet), lime tongs if limelight is used, pliers for changing carbons if the arc is to be the illuminant, screw-driver, matches, the key of the lantern box, and other similar items, are likely to be left behind unless such a list is made and carefully checked. On arriving at the hall, the first thing to be done as a rule is to get up the sheet, after which the professional operator generally begins to feel happy again.
The next thing, if it has not been done first, is to determine the position of the lantern, and this, as has been explained in Chapter VII, is a matter of the size of picture to be shown and the focus of the objective.
It is a mistake to show too large a picture; a little 'white' round the edges is a good thing, and it is better to have a small disc well illuminated than a large one less bright. Convenience, however, must also be considered, and it is often justifiable to go back a few feet farther than other considerations would dictate in order to place the lantern in a gallery or other spot where it is out of the way.
Having fixed the position of the lantern, it should be got into place, the cable or tubing connected or whatever else is necessary, according to the illuminant to be used. It should then be lit up, the flasher of the lens opened, and the light
centred sufficiently to produce some sort of disc upon the screen. (It is, of course, presumed that the lenses, &c., have previously been cleaned.)
A carrier should now be placed in the stage and a slide inserted into it, and the method of doing so requires a little explanation. The slide must be placed in the carrier upside down, as will be obvious to anyone who has studied Chapter VII, but in addition to this it must be turned the correct way, otherwise the picture will be reversed from left to right. This in the case of certain subjects, such as a copy of a picture, may not greatly matter; but in slides depicting buildings or landscapes with which the audience may be familiar, or worse still, printing or writing, is a serious blunder.
Slides made by a commercial firm will usually be 'spotted,' that is to say, will have two white spots on the face of the slide when the latter is viewed in its correct position, and at the top. The slides should be turned upside down and placed in the carrier with the spots, of course, now at the bottom and towards the condenser.
If a slide is not spotted it should be viewed as it is to appear on the screen, and then placed in the carrier with the face that was towards the operator as he viewed it turned to the condenser, and of course inverted.
The above remarks apply only in cases where the image is thrown on the screen; in the comparatively rare instances where it is shown through the latter the slides must be turned round laterally, but of course still inverted. The slide having been placed in the stage it should be 'focussed' by racking the objective in or out, and if necessary pulling out the draw tube as well until the image on the screen is sharply defined. So far the light has only been roughly centred, sufficiently so to enable the slide to be focussed, and to complete the operation both slide and carrier should next be taken out of the lantern, leaving a clear disc on the screen, and this disc may resemble any of the appearances shown in Fig. 50.
If it resembles A the light must be moved to the left, if like B to the right, like C it must be lowered, like D it must be raised, always moving it to the side opposite to the dark shade until this is central on the disc. If it now resembles E, the light must be moved nearer the condenser; if, on the contrary, the centre is dark, it must be drawn back until finally the circle should be as nearly as possible clear and bright all over, as at F.
It is important to note that this adjustment cannot be properly made while a slide is in position, and neither can it be made until the lantern has been focussed, so the above procedure is the only way to get a satisfactory result. With some of the larger illuminants, such as a paraffin-oil lamp, there are no centering adjustments, the size of the radiant rendering exact centering unnecessary, and generally speaking the smaller the luminous point, the more exact must the operation be.
In the case of such illuminants as acetylene or limelight
care must be taken that they are turned fully on before centering, otherwise turning on the fuller amount afterwards will raise the position of the luminous spot.
The centering achieved, the slide carrier may be replaced, the first slides placed in position, the remainder arranged in their proper order, the system of signalling with the lecturer determined, and all is ready.
If there is still an interval before commencing, the light may be switched off or turned out, or in the case say of limelight, turned down very low until wanted.
It is of extreme importance to see that all the slides are in their right order, though the duty of seeing to this usually rests with the lecturer rather than with the operator. I remember hearing of one lecture on the life of Queen Victoria, when the lecturer announced, 'The next picture will be a photograph of the Royal Prince who for many years shared the Throne with our gracious Sovereign.' At the words the operator brought on the next slide, which proved to be a restored specimen of a prehistoric monster (tableaux!). Such mistakes 'bring down the house,' but in serious lectures, and especially at religious services, cannot be too carefully guarded against.
Mention has already been made of the liability of moisture to condense on the surfaces of the condensers or slides, and to avoid this, so far as the condensers are concerned, it is well to light up say ten minutes before the lantern is actually wanted, or alternatively to take out the condensers and thoroughly warm them in front of a stove, or to place them wrapped in a cloth on hot-water pipes. The slides should in the same manner be warmed before using and should be finally held above the lantern or placed on the top, if this is flat, the last thing before being placed in the carrier. If these precautions are omitted, on a cold night the first surface of the condenser will become so covered with moisture as to almost obscure the slide, and this will quickly disappear
with the heat of the lantern. Next, the two inner surfaces of the condensers will behave in turn in the same way, and will take considerably longer to clear, especially if the ventilation of the condenser is poor; then the fourth surface will take up the running, and finally, when the lanternist is congratulating himself that the trouble is over, each successive slide will become affected in the same way. With an operator who knows his business, none of these troubles should occur.
Accidents.—These will occur sometimes, even in the best managed exhibition; the rubber tubing feeding a limelight jet gets kinked or trodden on, or a fuse melts if electric light is being used, &c., and out goes the light. In such cases a loud request such as, 'Would you mind turning up the light for a minute, please,' accompanied by a good-humoured laugh, usually allays the fears of 'nervy' people. An operator must never get 'nervy' himself. I have known of more than one fiasco because some little hitch occurred, and two or three timid ladies crowded round and asked anxious questions, till the lanternist lost his head. In one such case the cautious superintendent at a children's entertainment decided that it would be safer not to have the exhibition at all, simply because a regulator was not screwed tightly enough into a cylinder to prevent an escape of gas, only the operator (a somewhat youthful one) had been driven to the verge of lunacy by continual questions of the standard type, 'Are you sure it is safe?' 'Will it blow up?' 'Are you certain you understand it?' &c., &c. More serious accidents, such as the entire lantern getting upset, ought never to occur, and it is up to the lanternist to take whatever precautions he deems necessary to safeguard his instrument. With a juvenile audience, for example, it is often a good thing to arrange a barricade of forms round the lantern and to see that no one comes within it.
Finally, 'whatever is worth doing at all is worth doing well,' and this is as true of lantern exhibiting as of anything
else. There are a deplorable number of lantern exhibitions given with the sheet hanging in creases, dirty lenses, light poorly adjusted and centred, and occasionally slides shown upside down. A conscientious lanternist should see to every detail; slipshod methods, as in everything else, mean poor results.
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